In the ongoing effort to improve tire design, there is a recognized tension among tire performance, rolling resistance (or fuel economy), and treadwear. Typically, for use in a consumer tire, a tread compound is designed to optimized between these three considerations. However, efforts to improve for example fuel economy often lead to compromises in performance and/or treadwear. For higher performance tires desired by driving enthusiasts, the achievement better performance often comes with a compromise in treadwear or fuel economy. There is a desire therefore to develop tread compounds that can achieve improvement in any of performance, fuel economy, and treadwear with little or no compromise in the other two. One approach is in the elastomeric polymers used in the tread compound.
Aqueous solutions of a variety of polar aprotic polymers exhibit a lower critical solution temperature (LCST). When these solutions are heated above the LCST, the intramolecular hydrogen bonding is preferred compared to the hydrogen bonding with water molecules. This leads to collapse of the polymer coils and a precipitation of the polymer from solution. This phase transition is reversible so that the polymer redissolves when the temperature is again decreased below the LCST. A well-known example for an LCST polymer is poly(N-isopropyl acrylamide) (PNIPAM). Aqueous solutions of this polymer exhibit an LCST transition at about 33° C.
The combination of LCST polymers with elastomers offers the possibility of better control of elastomer performance in a variety of applications where the elastomer is exposed to water. Simple mixing of an LCST polymer with an elastomer results in a compound that will experience macrophase separation due to the lack of covalent bonds between the LCST polymer and the elastomer. Such a macrophase separation will most likely have a detrimental effect on tread compound properties.